Excavation Volume Calculator South Africa

Excavation volume formula

Sloped pit: V = D × (A bottom + 4 × A mid-depth + A top) ÷ 6. Box: V = L × W × D. Loose volume = bank volume × (1 + entered swell/100).

How do you calculate excavation volume?

For a rectangular vertical-sided excavation with a level bottom and level original surface, multiply the excavation length by width by vertical depth. Use the excavation dimensions, including any specified working space, rather than only the size of the footing, tank or structure. Keep all three dimensions in the same unit. The calculator converts metres, millimetres or feet to metres before calculating cubic metres. Separate excavations can be added only after checking they do not overlap.

Excavation volume calculator with slope

Choose the four-sided pit model when all four faces slope outward uniformly from a rectangular bottom. Enter the horizontal-to-vertical ratio for each pair of opposing faces: the width-direction ratio moves each long side outward, while the length-direction ratio moves each end outward. At height z above the bottom, the section is (L + 2 × mL × z) by (W + 2 × mW × z). Top length is L + 2 × mL × D and top width is W + 2 × mW × D. The bottom and top must be level, and the slopes straight and constant.

What does a slope of 1.5H to 1V mean?

For every metre of vertical depth, each affected face extends 1.5 metres horizontally outward. With 2 m depth, each side extends 3 m; two opposing sides therefore add 6 m to the top dimension. Enter 1.5, not 150, in the H:1V field. These are geometric ratios, not recommended excavation slopes. A ratio of zero represents a vertical face in the geometry only; it does not establish that a vertical face can stand safely.

Trench excavation with sloping sides

The trench model keeps both end faces vertical and applies the same entered outward slope to its two long sides. Its section area is D × (bottom width + mW × D); multiply by bottom length for volume. A pit with sloped ends needs the four-sided model instead. The trench model does not include ramps, benches, varying depths, curved alignments or additional end excavation. Calculate changes in geometry as distinct, non-overlapping sections or use survey quantities.

Prismoidal formula and the rectangular pit

The calculator uses V = D × (A bottom + 4 × A mid-depth + A top) ÷ 6 for the straight, uniformly sloped rectangular model. At mid-depth, dimensions are L + mL × D and W + mW × D. The section area varies quadratically with height, so this formula is exact for this ideal geometry. Multiplying the average of bottom and top areas by depth generally overestimates this four-sided model when both directions widen. The square-root frustum shortcut requires similar parallel sections and is not a universal formula for every sloped rectangular pit.

Worked soil excavation example

Suppose the bottom is 10 m long and 4 m wide, the vertical depth is 2 m, and each face uses an illustrative 1H:1V outward slope. The top is 14 m by 8 m, the mid-depth section is 12 m by 6 m, and the volume is 146.667 m³, rounded. The vertical-sided box with those bottom dimensions is 80 m³. This example shows the geometric difference only; it does not specify a safe slope for the site. A separately entered 20% swell gives 176 m³ loose volume.

Bank volume, loose soil and swell

Bank volume describes material in its original in-ground state. Loose volume estimates its bulk after excavation and handling. Enter the project-specific percentage increase relative to bank volume: loose = bank × (1 + swell/100). A swell input of 20 means a multiplier of 1.20, not 0.20. Zero means no adjustment has been entered, not that every soil has zero swell. Soil type, moisture and handling affect the conversion. Compacted backfill and shrinkage require their own specified basis and are not calculated here.

Truck loads, density and payload

Optional load planning assumes all estimated loose material is removed. Volume-only mode divides loose volume by the usable volume per load and rounds up. Combined mode also uses entered loose bulk density and usable payload, then takes the larger volume-based or mass-based whole-load count. Density must describe the loose material in tonnes per cubic metre; do not substitute bank density without conversion. A truck body capacity is not proof that filling it is within legal or vehicle limits. Confirm usable capacities and loading arrangements with the haulier.

Excavation costs and disposal quotes

Choose whether the excavation quote is per bank cubic metre or per loose cubic metre. Haulage per load uses the optional calculated load count, while disposal per loose cubic metre uses loose volume. Add separately quoted other costs once. Use one VAT basis and avoid charging again for haulage or disposal already included in another quote. Prices are entered arithmetic inputs, not live South African rates. Zero cost lines remain unpriced. Retained soil, contamination, disposal acceptance, rock breaking, dewatering and minimum charges can change the actual scope.

Uneven ground, surveys and site assessment

This tool models level top and bottom planes with constant depth and straight faces. It does not calculate a varying natural-ground surface, a survey cut-and-fill difference, stepped benches, overbreak or intersecting trenches. For those conditions, obtain a measured quantity or divide the work into appropriate non-overlapping sections using the project’s measurement method. Excavation stability, shoring, access, buried services, water and nearby structures need a competent site assessment. A volume result does not approve an excavation method or determine a safe slope.

Reviewed by the 99tools team. Editorial and corrections policy.

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Soil excavation guides

• How to Calculate Excavation Volume with Slope
• Soil Excavation: Bank Volume, Loose Volume and Truck Loads